Marley was enjoying a romp at the park and I realized it was really late.  I gathered all of our things and as I reached the gate I realized there was a dog inside the double gate structure.  I looked around for the dog owner and after a few minutes realized nobody was heading in our direction.  The dog was scared and kept trying to get out.  I went in and checked the dog for a collar, which he was wearing but had no tags.  We let him into the park, to keep him from escaping and allow other people to enter and exit.
I asked everybody if they owned the dog.  Everybody was shocked the dog had been abandoned at the park; however, nobody offered to help.  By this time it is quite late and I have no idea what to do with a large abandoned dog.
I start calling everybody I know asking for assistance.  I keep hoping somebody will say, "I'll be right over, I'll take care of it."  Nobody does, however everybody has a lot of great ideas.  I call the county shelter and their after hours response leaves a lot to be desired.
At this point the park is pretty empty and I decide to take him to the Emergency Vet to check for a microchip. I've also heard a rumor that they will keep found animals overnight.  Turns out the dog does not have a microchip and the Vet will not accept the dog overnight.
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| Found dog: Blue eyed border collie | 
The receptionist takes a few photos of the found dog and my contact information and wishes me luck.
 
I find myself sitting in the reception area wondering what to do?  I don't know this dog and while he seems calm, I know he is scared and therefore unpredictable.  I do not want to expose Marley or Bob to an unpredictable dog.  
What would you do in this situation?